class_docstr: Base class for DataFlow that proxies another.
  Every method is proxied to ``self.ds`` unless overriden by a subclass.
code: def __iter__(self):
      return self.ds.__iter__()
  
imports: import threading
  from abc import ABCMeta, abstractmethod
  import six
  from ..utils.utils import get_rng
label_desc: Use image node_id 4 for calling the ProxyDataFlow obj's underlying member method code with example usage: obj.__iter__() and returns: self